Influence des pretraitements par KCl et des rapports Ca/Na du milieu sur la croissance de vitroplants de tomate en milieu NaCl

The 18-day-old tomato vitroplants were obtained in axenic conditions by culture of expiants (including the terminal bud and the last internode of the stem) on agar-agar nutritive medium with 0 or 75 mM NaCl. The growth and the mineral content of the vitroplants were compared when the expiants were grown on media either with low or high K/Na and Ca/Na ratios, or with low K/Na and Ca/Na ratios after pretreatments of expiants by KC1, NaCl or CaCl₂ (from 0 to – 4.5 bar). The KCl pretreatment (-1.1 bar) during one day brings about an increase in vitroplant growth greater than that produced by a high Ca/Na ratio medium. The Cl accumulation was similar in expiants pretreated by KCl or NaCl. Ion content per gram of fresh matter was similar in 18-day-old vitroplants pretreated by KCl, NaCl or CaCl₂; the Na accumulation by KC1 pretreated vitroplants was not lower than that of 18-day-old vitroplants grown on a high Ca/Na ratio medium. These results show the relation between Na content of expiants and the growth of vitroplants in a NaCl medium.     

等渗Ca(NO3)2和NaCl胁迫对黄瓜幼苗生长及渗透调节物质含量的影响

采用营养液培养方法,以耐盐性较弱的‘津春2号’黄瓜品种为试材,研究了等渗Ca(NO3)2和NaCl胁迫对黄瓜幼苗生长、根系电解质渗透率、根系活力、Na+和K+含量及渗透调节物质含量的影响。结果显示:(1)在84mmol.L-1 NaCl和56mmol.L-1 Ca(NO3)2等渗胁迫下,黄瓜幼苗鲜重和干重均显著下降,且NaCl处理下降的幅度大于等渗Ca(NO3)2处理。(2)NaCl主要通过对黄瓜根系的伤害来抑制植株生长,表现为根系活力下降、根系质膜透性增大、Na+大量积累、K+含量显著下降、Na+/K+明显上升,最终导致根冠比下降;而Ca(NO3)2处理对根系质膜透性、K+含量、Na+/K+的影响均小于NaCl胁迫,且根系活力和根冠比上升,但Ca(NO3)2胁迫后叶片含水量和渗透调节能力均小于NaCl胁迫。(3)NaCl胁迫条件下,黄瓜幼苗内渗透调节物质以可溶性糖为主,而Ca(NO3)2胁迫以可溶性蛋白为主。研究表明,NaCl胁迫对黄瓜幼苗的伤害大于等渗Ca(NO3)2,NaCl主要通过破坏根系质膜结构影响植株生长,而Ca(NO3)2主要通过引起地上部生理干旱来影响植株生长。     

The ATP4- receptor-operated ion channel of human lymphocytes: inhibition of ion fluxes by amiloride analogs and by extracellular sodium ions.

Extracellular ATP is known to increase the membrane permeability of a variety of cells. Addition of ATP to human leukemic lymphocytes loaded with the Ca2+ indicator, fura-2, induced a rise in cytosolic Ca2+ concentration which was attenuated or absent in NaCl media compared with KCl, choline Cl, or NMG Cl media. In contrast, anti-immunoglobulin antibody gave similar Ca2+ transients in NaCl and KCl media. A half-maximal inhibition of peak ATP-induced Ca2+ response was observed at 10-16 mM extracellular Na+. Basal 45Ca2+ influx into lymphocytes was stimulated 9.6-fold by ATP added to cells in KCl media, but the effect of ATP was greatly reduced for cells in NaCl media. Hexamethylene amiloride blocked 74% of the ATP-stimulated Ca45 uptake of cells in KCl media. Flow cytometry measurements of fluo-3-loaded cells confirmed that the ATP-induced rise in cytosolic Ca2+ was inhibited either by extracellular Na+ or by addition of hexamethylene amiloride. Extracellular ATP stimulated 86Rb efflux from lymphocytes 10-fold and this increment was inhibited by the amiloride analogs in a rank order of potency 5-(N-methyl-N-isobutyl)amiloride greater than 5-(N,N-hexamethylene)amiloride greater than 5-(N-ethyl-N-isopropyl)amiloride greater than amiloride. ATP-induced 86Rb efflux showed a sigmoid dependence on the concentration of ATP and Hill analysis gave K1/2 of 90 and 130 microM and n values of 2.5 and 2.5 for KCl and NaCl media, respectively. However, the maximal ATP-induced 86Rb efflux was 3-fold greater in KCl than in NaCl media. Raising extracellular Na+ from 10 to 100 mM increased ATP-induced Na+ influx from a mean of 2.0 to 3.7 nEq/10(7) cells/min, suggesting either saturability or self-inhibition by Na+ of its own influx. These data suggest that ATP opens a receptor-operated ion channel which allows increased Ca2+ and Na+ influx and Rb+ efflux and these fluxes are inhibited by extracellular Na+ ions as well as by the amiloride analogs.     

等渗NaCL和KCL胁迫对高梁幼苗生长和气体交换的影响

本文比较研究了等渗NaCl和KCl胁迫下,高粱幼苗生长及叶片离子含量、质膜相对透性和有关气体交换参数的变化。结果表明,在低浓度NaCl和KCl胁迫7天时,高粱生长、含水量和质膜相对透性与对照相比没有明显变化,而净光合速率、蒸腾速率和气孔导度已明显下降,叶肉细胞间隙CO2浓度明显增加。NaCl胁迫下叶片Na+含量成倍增加,而K+和Ca2+含量无明显变化。KCl胁迫时叶片K+含量明显增加,Ca2+含量明显下降,而Na+含量没有明显变化。随着NaCl或KCl浓度的增加,幼苗生长和叶片含水量明显下降,质膜透性和细胞间隙CO2浓度明显增加,净光合速率、蒸腾速率和气孔导度进一步下降。 NaCl胁迫下叶片Na+含量进一步增加,K+和Ca2+进一步下降,而KCl胁迫下叶片K+含量进一步 增加,Na+和Ca2+含量进一步下降。KCl对高粱生长抑制、质膜透性、Ca2+含量下降及光合气体交换参数的影响均明显大于等渗的NaCl。     

Nutritional requirements of Plasmodium falciparum in culture. I. Exogenously supplied dialyzable components necessary for continuous growth

Continuous cultivation of Plasmodium falciparum presently requires the nutritionally complex medium, RPMI 1640. A basal medium of KCl, NaCl, Na2HPO4, Ca(NO3)2, MgSO4, glucose, reduced glutathione, HEPES buffer, hypoxanthine, phenol red (in RPMI 1640 concentrations), and 10% (v/v) exhaustively dialyzed pooled human serum was used to determine which vitamins and amino acids had to be exogenously supplied for continuous cultivation. Supplementation of basal medium with calcium pantothenate, cystine, glutamate, glutamine, isoleucine, methionine, proline, and tyrosine was necessary for continuous growth. This semi-defined minimal medium supported continuous growth of four isolates of P. falciparum at rates slightly less than those obtained with RPMI 1640. Adding any other vitamin or amino acid did not improve growth. Incorporation of several non-essential amino acids, particularly phenylalanine and leucine, into proteins was markedly enhanced in the minimal medium compared to RPMI 1640.     

Evidence for extensive methylation of ribosomal RNA genes in a rat XC cell line

The effects of extracellular Na+, K+ and Cl- on neurite outgrowth of PC12 pheochromocytoma cells were studied. Nerve growth factor (NGF)-induced neurite formation was inhibited upon substitution of choline chloride for NaCl under normal culture conditions. It was found that neurite formation increased proportionately with the concentration of Na+ in medium up to 150 mM. When PC12 cells were exposed to NGF in suspension culture followed by transfer to new dishes, they showed neurite extention in response to NGF in an RNA- and protein synthesis-independent manner. Under these conditions, neurite outgrowth occurred normally in 60-150 mM Na+, whereas it decreased significantly at lower concentrations of Na+. Na+ dependency was also observed for cyclic AMP-mediated neurite formation of PC12 cells. In contrast neurite outgrowth was independent of K+ in the range 5-106 mM, suggesting that membrane potential did not play a role in this process. No alterations were observed in neurite outgrowth with Cl- replaced by NO3-, SO2-4, or 2-hydroxyethanesulfonate. Thus, extracellular Na+ plays a role in controlling neurite formation of these cells. An attempt was made to relate this effect to a decrease in cytoplasmic Ca2+ concentration monitored by a fluorescent dye sensitive to Ca2+.     

Protein phosphatase type 2B (calcineurin)-mediated, FK506-sensitive regulation of intracellular ions in yeast is an important determinant for adaptation to high salt stress conditions.

To assess the physiological function of Ca(2+)-dependent protein phosphatase (PP2B) in the yeast Saccharomyces cerevisiae, the phenotypes of PP2B-deficient mutants were investigated. Although PP2B was dispensable for growth under normal conditions, the mutations did, however, cause growth inhibition under certain stress circumstances. The growth of the mutants was inhibited by NaCl and LiCl, but not by KCl, CaCl2, MgCl2 or nonspecific osmotic stresses. Upon shift to high NaCl medium, intracellular Na+ levels of both wild type yeast and the mutants initially increased at a comparable rate. However, internal Na+ in wild type cells started to decline more rapidly than the mutant cells during cultivation in high NaCl medium, indicating that PP2B is important in maintaining a gradient across the membrane. The protection against salt stress was achieved, at least in part, by the stimulation of Na+ export. The maintenance of a high level of internal K+ in high NaCl medium was also PP2B-dependent. In the presence of the immunosuppressant FK506, the growth behaviour and intracellular Na+ and K+ of wild type cells in high NaCl medium became very similar to those of the PP2B-deficient mutant in a manner dependent on the presence of the FK506 binding protein.     

Sodium/calcium exchange in smooth-muscle microsomal fractions.

The existence of Na+ -dependent Ca2+ transport was investigated in microsomal fractions from the longitudinal smooth muscle of the guinea-pig ileum and from the rat aorta, and its activity was compared with that of the plasmalemmal ATP-dependent Ca2+ pump previously identified in these preparations. The rate of Ca2+ release from plasmalemmal vesicles previously loaded with Ca2+ through the ATP-dependent Ca2+ pump was transiently faster in the presence of 150 mM-NaCl in the medium than in the presence of 150 mM-KCl or -LiCl or 300 mM-sucrose. Na+-loaded vesicles took up Ca2+ when an outwardly directed Na+ gradient was formed across the membrane. The Ca ionophore A23187 induced a rapid release of 85% of the sequestered Ca2+, whereas only 15% was displaced by La3+. Ca2+ accumulated by the Na+-induced Ca2+ transport was released by the addition of NaCl, but not KCl, to the medium. Ca2+ uptake in Na+-loaded vesicles was inhibited in the presence of increasing NaCl concentration in the medium. Half-maximum inhibition was observed with 28 mM-NaCl. Data fitted the Hill equation, with a Hill coefficient (h) of 1.9. Na+-induced Ca2+ uptake was a saturable function of Ca2+ concentration in the medium. Half-maximum activity was obtained with 18 microM-Ca2+ in intestinal-smooth-muscle microsomal fraction and with 50 microM-Ca2+ in aortic microsomal fraction. The results suggest that in these membrane preparations a transmembrane movement of Ca2+ can be driven by a Na+ gradient. However, the Na+-induced Ca2+ transport had a lower capacity, a lower affinity and a slower rate than the ATP-dependent Ca2+ pump.     

Dependence of GnRH action on Na+, K+, and Ca2+ in the frog, Rana pipiens, pituitary

The roles of K+, Ca2+, and Na+ ions in the mechanism of gonadotropin releasing hormone (GnRH) action on frog (Rana pipiens) hemipituitaries were studied using an in vitro superfusion system. The effects of elevated K+ alone or in combination with Ca2+-depleted medium, tetrodotoxin (TTX), or with 100 ng/ml GnRH were examined. The involvement of K+ was also studied indirectly through the use of tetraethyl ammonium chloride (TEA). The importance of Ca2+ was established by the loss of responsiveness to GnRH in Ca2+-depleted medium, or in the presence of the Ca2+ competitor CoCl2. The absence of a major dependence of GnRH on Na+ was revealed by the continued gonadotropin secretion after addition of 1 microM TTX to medium containing GnRH or 36.3 mM KCl, or by replacement of NaCL with choline chloride. High (10 X normal) KCl (36.3 mM) stimulated gonadotropin--both LH and FSH--secretion, but the response was more gradual than for GnRH. The inclusion of TEA (to block K+ efflux) in medium with GnRH accentuated the effect of GnRH, and the effects of elevated (36.3 mM) KCl and 100 ng/ml GnRH (a relatively high dose) were additive. Responses to high K+, like GnRH, were abolished by removal of Ca2+ from the medium. Overall, the roles of K+, Ca2+, and Na+ ions in the mechanism of GnRH action are very similar between mammals and frogs; Ca2+ apparently serves a critical function in the mechanism of GnRH action, while Na+ appears not to be involved. K+ can induce gonadotropin secretion, but it is not clear that it plays a direct role in the mediation of the action of GnRH.     

Cyclic GMP stimulates Na+/Ca2+ exchange in vascular smooth muscle cells in primary culture.

We examined the effect of cGMP on Na+/Ca2+ exchange in rat aortic smooth muscle cells (VSMCs) in primary culture. The intracellular Ca2+ concentration [( Ca2+]i) was raised by adding ionomycin to VSMCs incubated at high extracellular pH (pH0) (pH0 = 8.8) and high extracellular Mg2+ (Mg2+0) (Mg2+0 = 20 mM), conditions that inhibit activity of the sarcolemmal Ca2+ pump. 45Ca2+ efflux observed under these conditions was mostly extracellular Na+ (Na+0)-dependent and thus presumably catalyzed by the Na+/Ca2+ exchanger. Brief treatment of VSMCs with 8-bromo-cGMP or atrial natriuretic peptide increased this Na+0-dependent 45Ca2+ efflux by about 50%. The 8-bromo-cGMP treatment did not significantly influence total cell Na+, membrane potential, and cell pH. Conversely, when VSMCs were loaded with Na+ and then exposed to a Na+0-free medium, the rate of 45Ca2+ uptake into VSMCs increased as cell Na+ increased. Prior treatment of VSMCs with 8-bromo-cGMP accelerated 45Ca2+ uptake by up to 60% without influencing Na+ loading itself. Treatment of VSMCs with 25 microM 2,5-di-(tert-butyl)-1,4-benzohydroquinone, an inhibitor of the sarcoplasmic reticulum Ca(2+)-ATPase, induced a transient elevation of [Ca2+]i. 8-Bromo-cGMP stimulated the rate of recovery phase of this Ca2+ transient measured in the high pHo/high Mg2+o medium. All these results indicate that cGMP stimulates Na+/Ca2+ exchange in VSMCs.     

Sodium-calcium exchange in membrane vesicles from Artemia

Membrane vesicles were prepared from Artemia nauplii (San Francisco Bay variety) 45 h after hydration of the dry cysts. Na+-loaded vesicles accumulated up to 10 nmol Ca2+/mg protein when diluted 50-fold into 160 mM KCl containing 15 microM CaCl2. Practically no accumulation of Ca2+ was observed if the vesicles were diluted into 160 mM NaCl instead of KCl, or if they were treated with monensin, a Na+ ionophore, for 30 s prior to addition of CaCl2 to the KCl medium. These observations indicate that the Artemia vesicles exhibit Na-Ca exchange activity. The velocity of Ca2+ accumulation by the vesicles in KCl was stimulated 2.6-fold by the K+ ionophore valinomycin, suggesting that the exchange system is electrogenic, with a stoichiometry greater than 2Na+ per Ca2+. Km,Ca and Vmax values were 15 microM and 7.5 nmol/mg protein.s, respectively. Exchange activity in the Artemia vesicles was inhibited by benzamil (IC50 approximately equal to 100 microM) and by quinacrine (IC50 approximately equal to 250 microM), agents that also inhibit exchange activity in cardiac sarcolemmal vesicles. Unlike cardiac vesicles, however, exchange activity in Artemia was not stimulated by limited proteolysis, redox reagents, or intravesicular Ca2+. This indicates that the two exchange systems are regulated by different mechanisms. Vesicles were prepared from Artemia at various times after hydration of the dry cysts and examined for exchange activity. Activity was first observed at approximately 10 h after hydration and increased to a maximal value by 30-40 h; hatching of the free swimming nauplii occurred at 18-24 h. The results suggest that hatching Artemia nauplii might be a particularly rich source of mRNA coding for the Na+-Ca2+ exchange carrier.     

等渗NaCl和KCl胁迫对高粱幼苗生长和气体交换的影响

本文比较研究了等渗ＮａＣｌ和ＫＣｌ胁迫下,高粱幼苗生长及叶片离子含量、质膜相对透性和有关气体交换参数的变化。结果表明,在低浓度ＮａＣｌ和ＫＣｌ胁迫７天时,高粱生长、含水量和质膜相对透性与对照相比没有明显变化,而净光合速率、蒸腾速率和气孔导度已明显下降,叶肉细胞间隙ＣＯ２浓度明显增加。ＮａＣｌ胁迫下叶片Ｎａ＋含量成倍增加,而Ｋ＋和Ｃａ２＋含量无明显变化。ＫＣｌ胁迫时叶片Ｋ＋含量明显增加,Ｃａ２＋含量明显下降,而Ｎａ＋含量没有明显变化。随着ＮａＣｌ或ＫＣｌ浓度的增加,幼苗生长和叶片含水量明显下降,质膜透性和细胞间隙ＣＯ２浓度明显增加,净光合速率、蒸腾速率和气孔导度进一步下降。ＮａＣｌ胁迫下叶片Ｎａ＋含量进一步增加,Ｋ＋和Ｃａ２＋进一步下降,而ＫＣｌ胁迫下叶片Ｋ＋含量进一步增加,Ｎａ＋和Ｃａ２＋含量进一步下降。ＫＣｌ对高粱生长抑制、质膜透性、Ｃａ２＋含量下降及光合气体交换参数的影响均明显大于等渗的ＮａＣｌ。     

Site density of the sodium-calcium exchange carrier in reconstituted vesicles from bovine cardiac sarcolemma

The site density of the Na2+-Ca2+ exchanger in bovine cardiac sarcolemma was estimated from measurements of the fraction of reconstituted proteoliposomes exhibiting exchange activity. Sarcolemmal vesicles were solubilized with 1% Triton X-100 in the presence of either 100 mM NaCl or 100 mM KCl; after a 20-40-min incubation period on ice, sufficient KCl, NaCl, CaCl2, and soybean phospholipids were added to each extract to give final concentrations of 40 mM NaCl, 120 mM KCl, 0.1 mM CaCl2, and 10 mg/ml phospholipid. These mixtures were then reconstituted into proteoliposomes, and the rate of 45Ca2+ isotopic exchange was measured under equilibrium conditions. Control studies showed that Na+-Ca2+ exchange activity was completely lost if Na+ was not present during solubilization. The difference in 45Ca2+ uptake between vesicles initially solubilized in the presence or absence of NaCl therefore reflected exchange activity and corresponded to 3.1 +/- 0.3% of the total 45Ca2+ uptake by the entire population of vesicles, as measured in the presence of the Ca2+ ionophore A23187. Assuming that each vesicle with exchange activity contained 1 molecule of the Na+-Ca2+ exchange carrier, a site density of 10-20 pmol/mg of protein for the exchanger was calculated. The Vmax for Na+-Ca2+ exchange activity in the proteoliposomes was approximately 20 nmol/mg of protein.s which indicates that the turnover number of the exchange carrier is 1000 s-1 or more. Thus, the Na+-Ca2+ exchanger is a low density, high turnover transport system.     

Electrical characteristics in an excitable element of lipid membrane.

Electrical characteristics in a membrane constructed from a porous filter adsorbed with a lipid analogue, dioleoyl phosphate (DOPH), were investigated in a situation interposed between 100 mM NaCl + 3 mM CaCl2 and 100 mM KCl. Calcium ions affected significantly the membrane characteristics. The membrane potential was negative on the KCl side, which implies the higher permeability to K+ than Na+; this tendency was increased by a tiny amount of Ca2+. While the membrane showed a low electrical resistance of several k omega . cm2 under K+/Na+ gradient, it showed several M omega . cm2 by Ca2+. The surface structure of the membrane exhibited many voids in the low-resistance state, but the surface was covered by oil droplets in the high-resistance state. Oscillations of the membrane potential appeared spontaneously with application of the electrical current from the KCl side to the NaCl + CaCl2 side. The frequency was increased with the electrical current. All these results were explained comprehensively using an electrochemical kinetic model taking account of the Ca2+ binding effect, where DOPH assemblies make a phase transition between oil droplets due to Ca2+ and multi-bilayers with excess K+. The oscillation arises from coupling of the phase transition to accumulation and release of K+ or Ca2+. This membrane can be used as an excitable element regulated by Ca2+ in neuro-computer devices.     

Some properties of transport ATPases in functionally different muscles]

The properties of Ca-transporting system in sarcoplasmic reticulum membranes in fast and slow frog muscles as well as some properties of sarcolemma Na, K-ATPase of the same object were investigated. The rate of Ca2+ uptake, Ca-ATPase activity and Ca/ATP ratio for the reticulum of fast muscle demonstrated higher values than those for the reticulum of slow muscle. The rate of Ca2+ accumulation by the fragments of the rectus reticulum and Ca/ATP ratio were found to decrease under the influence of acetylcholine (0.05-5 mM). The transport system of the sartorius reticulum was found to be less sensitive to acetylcholine. The peak activity of Na, K-ATPase in femoral muscles of the frog occurred at 80 mM NaCl and 60 mM KCl, whereas in the rectus abdominal muscle it equalled 100 mM NaCl and 40 mM KCl. Thus, Na, K-ATPase activity in the slow muscle was predominantly higher than that in the mixed (femoral) muscles. If the sarcolemma preparations of the muscles of both types the inhibitory effect of acetylcholine on Na; K-ATPase was registered. The enzyme of slow muscles exhibited higher sensibility to acetylcholine.     

Role of separate K+ and Cl- channels and of Na+/Cl- cotransport in volume regulation in Ehrlich cells

Cells resuspended in hypotonic medium initially swell as nearly perfect osmometers, but later recover their volume with an associated KCl loss. This regulatory volume decrease (RVD) is unaffected when nitrate is substituted for Cl- or if bumetanide or 4,4'-diisothiocyanostilbene-2,2'-disulfonate (DIDS) is added. It is inhibited by quinine, Ba2+, low pH, anticalmodulin drugs, and depletion of intracellular Ca2+. It is accelerated by the Ca2+ ionophore A23187, or by a sudden increase in external Ca2+ and at high pH. A net KCl loss is also seen after addition of ionophore A23187 in isotonic medium. Similarities are demonstrated between the KCl loss seen after addition of A23187 and the KCl loss seen during RVD. It is proposed that separate conductive K+ and Cl- channels are activated during RVD by release of Ca2+ from internal stores, and that the effect is mediated by calmodulin. After restoration of tonicity the cells shrink initially, but recover their volume with an associated KCl uptake. This regulatory volume increase (RVI) is inhibited when NO3- is substituted for Cl-, and is also inhibited by furosemide or bumetanide, but it is unaffected by DIDS. The unidirectional Cl-flux ratio is compatible with either a coupled uptake of Na+ and Cl-, or an uptake via a K+/Na+/2Cl- cotransport system. No K+ uptake was found, however, in ouabain-poisoned cells where a bumetanide-sensitive uptake of Na+ and Cl- in nearly equimolar amounts was demonstrated. Therefore, it is proposed that the primary process during RVI is an activation of an otherwise quiescent Na+/Cl- cotransport system with subsequent replacement of Na+ by K+ via the Na+/K+ pump. There is a marked increase in the rate of pump activity in the absence of a detectable increase in intracellular Na+ concentration.     

Extracellular Ca²+ alleviates NaCl-induced stomatal opening through a pathway involving H₂O₂-blocked Na+ influx in Vicia guard cells

To gain further insights into the function of extracellular Ca2+ in alleviating salt stress, Vicia faba guard cell protoplasts (GCPs) were patch-clamped in a whole-cell configuration. The results showed that 100 mM NaCl clearly induced Na+ influx across the plasma membrane in GCPs and promoted stomatal opening. Extracellular Ca2+ at 10 mM efficiently blocked Na+ influx and inhibited stomatal opening, which was partially abolished by La3+ (an inhibitor of plasma membrane Ca2+ channel) or catalase (CAT, a H?O? scavenger), respectively. These results suggest that the plasma membrane Ca2+ channels and H?O? possibly mediate extracellular Ca2+-blocked Na+ influx in GCPs. Furthermore, extracellular Ca2+ activated the plasma membrane Ca2+ channels under NaCl stress, which was partially abolished by CAT. These results, taken together, indicate that hydrogen peroxide (H?O?) likely regulates Na+ uptake by activating plasma membrane Ca2+ channels in GCPs. In accordance with this hypothesis, H?O? could mimic extracellular Ca2+ to activate Ca2+ channels and block Na+ influx in guard cells. A single-cell analysis of cytosolic free Ca2+ ([Ca2+](cyt)) using Fluo 3-AM revealed that extracellular Ca2+ induced the accumulation of cytosolic Ca2+ under NaCl stress, but had few effects on the accumulation of cytosolic Ca2+ under non-NaCl conditions. All of these results, together with our previous studies showing that extracellular Ca2+ induced the generation of H?O? in GCPs during NaCl stress, indicate that extracellular Ca2+ alleviates salt stress, likely by activating the H?O?-dependent plasma membrane Ca2+ channels, and the increase in cytosolic Ca2+ appears to block Na+ influx across the plasma membrane in Vicia guard cells, leading to stomatal closure and reduction of water loss.     

Significance of regional difference in ion concentrations in lizard, Hemidactylus flaviviridis (Rüppell): assessment of ionic influence on sperm motility in vitro

A gradual increase in the concentration of Ca2+ from anterior to the posterior region was observed when mono- and divalent cations were estimated in different segments of the epididymis in wall lizard. Na+ and K+ levels increased from anterior to middle segment but declined significantly in the posterior segment. However, no significant difference in the levels of Mg2+ was observed in various segments. To study the influence of mono- and divalent cations on sperm motility in vitro, the spermatozoa from posterior region of the epididymis were incubated in medium with varying concentrations of Na+, K+, Ca2+ and Mg2+. Spermatozoa were non-motile when suspended in Na+-free medium. Addition of NaCl induced the acquisition of sperm motility in a concentration-dependent manner. Further, amiloride, a Na+-influx blocker, markedly reduced the Na+-induced forward progressive motility. Unlike Na+, the presence of K+ or Ca2+ in the incubation medium reduced the motility of spermatozoa even at very low concentrations. The inhibitory effect of Ca2+ decreased when nifedipine, a Ca2+-influx blocker, was added to the medium. Mg2+ at high concentrations only was able to reduce the forward progressive motility.     

Calcium ion binding to lobster nerve membranes

The binding of 45Ca2+ to membrane material isolated from lobster walking leg nerves was studied using a rapid filtration technique. In solutions of high ionic strength (450 mM), the amount of 45Ca2+ bound to this membrane material was found to be highly dependent on the monovalent cation used in the incubating solution. The amount of 45Ca2+ bound was larger when the membranes were incubated in a KCl solution compared to when they were incubated in a NaCl solution. This difference was attributed to the ability of these closed membrane vesicles to accumulate Ca2+ into the vesicle when incubating in a KCl solution but not in a NaCl solution. This accumulation of Ca2+ was found to be independent of metabolic energy and depended primarily on the absence of Na+ from the incubation medium. At low ionic strength, the membranes formed open fragments and the amount of Ca2+ bound was no longer sensitive to the monovalent cation species in the incubation solution. The 45Ca2+ bound under these low ionic strength conditions was considered to be bound to anionic sites on the membranes.     

Augmentation of vasopressin-induced cAMP production by high potassium in rat renal papillary collecting tubule cells in culture.

The effect of high potassium, 60 mM KCl, on the cellular action of arginine vasopressin (AVP) was studied in rat renal papillary collecting tubule cells in culture. In the presence of 0.5 mM 3-isobutyl-1-methylxanthine AVP-induced cAMP production was enhanced by pretreatment of the cells with 60 mM KCl. Such an enhancement was not found in cells pretreated with Ca(2+)-free medium containing 1 mM EGTA or in Na(+)-free medium, which rather reduced AVP-induced cAMP production. Similar results were obtained with the blockers of cellular Ca2+ uptake, 1 x 10(-4) M verapamil and 1 x 10(-5) M nifedipine. The 60 mM KCl elevated the cellular sodium concentration ([Na+]i) from 15.1 to 18.8 mM, cellular pH (pHi) from 7.18 to 7.32, and basal cellular free calcium concentration ([Ca2+]i). These results indicate that high potassium promptly augments AVP-induced cAMP production in renal papillary collecting tubule cells. This effect is based on the alkalinized pHi and the increased [Ca2+]i.